jurt/com/sun/star/uno/WeakReference.java

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  30
  31 package com.sun.star.uno;
  32
  33 import com.sun.star.uno.XWeak;
  34 import com.sun.star.uno.UnoRuntime;
  35 import com.sun.star.uno.XAdapter;
  36 import com.sun.star.uno.XReference;
  37
  38 /** This class holds weak reference to an object. It actually holds a reference to a
  39     com.sun.star.XAdapter implementation and obtains a hard reference if necessary.
  40  */
  41 public class WeakReference
  42 {
  43     private final boolean DEBUG= false;
  44     private OWeakRefListener m_listener;
  45     // There is no default constructor. Every instance must register itself with the
  46     // XAdapter interface, which is done in the constructors. Assume we have this code
  47     // WeakReference ref= new WeakReference();
  48     // ref = someOtherWeakReference;
  49     //
  50     // ref would not be notified (XReference.dispose()) because it did not register
  51     // itself. Therefore the XAdapter would be kept aliver although this is not
  52     // necessary.
  53
  54     /** Creates an instance of this class.
  55      *@param obj - another instance that is to be copied
  56      */
  57     public WeakReference(WeakReference obj)
  58     {
  59         if (obj != null)
  60         {
  61             Object weakImpl= obj.get();
  62             if (weakImpl != null)
  63             {
  64                 XWeak weak= UnoRuntime.queryInterface(XWeak.class, weakImpl);
  65                 if (weak != null)
  66                 {
  67                     XAdapter adapter= (XAdapter) weak.queryAdapter();
  68                     if (adapter != null)
  69                         m_listener= new OWeakRefListener(adapter);
  70                 }
  71             }
  72         }
  73     }
  74
  75     /** Creates an instance of this class.
  76      *@param obj XWeak implementation
  77      */
  78     public WeakReference(Object obj)
  79     {
  80         XWeak weak= UnoRuntime.queryInterface(XWeak.class, obj);
  81         if (weak != null)
  82         {
  83             XAdapter adapter= (XAdapter) weak.queryAdapter();
  84             if (adapter != null)
  85                 m_listener= new OWeakRefListener(adapter);
  86         }
  87     }
  88     /** Returns a hard reference to the object that is kept weak by this class.
  89      *@return a hard reference to the XWeak implementation.
  90      */
  91     public Object get()
  92     {
  93         if (m_listener != null)
  94             return m_listener.get();
  95         return null;
  96     }
  97 }
  98
  99 /** Implementation of com.sun.star.uno.XReference for use with WeakReference.
 100  *  It keeps the XAdapter implementation and registers always with it. Deregistering
 101  *  occurs on notification by the adapter and the adapter is released.
 102  */
 103 class OWeakRefListener implements XReference
 104 {
 105     private final boolean DEBUG= false;
 106     private XAdapter m_adapter;
 107
 108     /** The constructor registered this object with adapter.
 109      *@param adapter the XAdapter implementation.
 110      */
 111     OWeakRefListener( XAdapter adapter)
 112     {
 113         m_adapter= adapter;
 114         m_adapter.addReference(this);
 115     }
 116     /** Method of com.sun.star.uno.XReference. When called, it deregisteres this
 117      *  object with the adapter and releases the reference to it.
 118      */
 119     synchronized public void dispose()
 120     {
 121         if (m_adapter != null)
 122         {
 123             m_adapter.removeReference(this);
 124             m_adapter= null;
 125         }
 126     }
 127
 128     /** Obtains a hard reference to the object which is kept weak by the adapter
 129      *  and returns it.
 130      *  @return hard reference to the otherwise weakly kept object.
 131      */
 132     synchronized Object get()
 133     {
 134         Object retVal= null;
 135         if (m_adapter != null)
 136         {
 137             retVal= m_adapter.queryAdapted();
 138             if (retVal == null)
 139             {
 140                 // If this object registered as listener with XAdapter while it was notifying
 141                 // the listeners then this object might not have been notified. If queryAdapted
 142                 // returned null then the weak kept object is dead and the listeners have already
 143                 // been notified. And we missed it.
 144                 m_adapter.removeReference(this);
 145                 m_adapter= null;
 146             }
 147         }
 148         return retVal;
 149     }
 150 }